The present invention relates to a method for production and purification of phenol.
The cumene-to-phenol industrial method is well known and involves a two step synthesis: air-oxidation of cumene to a cumene hydroperoxide (CHP) intermediate, followed by acidic decomposition (cleavage) of the CHP by contacting it with an acid catalyst such as sulfuric acid to yield phenol and acetone as principle products. However, in addition to the desired products, the resulting crude cleavage product mixture also contains amounts of various by-products including alpha-methylstyrene, acetophenone, cumylphenol, dimethylbenzyl alcohol, unreacted cumene and traces of various xe2x80x9ccarbonyl-typexe2x80x9d impurities including hydroxyacetone, mesityl oxide and aldehydes. During the subsequent purification steps these undesirable by-products and impurities must be removed from the final product phenol and acetone using various separation methods which include extraction, distillation and catalytic chemical treatment.
The hydroxyacetone (HA) impurity is known to be produced at the CHP cleavage step via oxidation of acetone at concentrations of 1000 to 2500 ppm, depending on the operating conditions employed. When the CHP cleavage mixture, containing sulfuric acid catalyst, is neutralized, the HA present in the mixture equilibrates and partitions into the two phases in the neutralizer vessel in about equal concentrations. HA is particularly difficult to remove from phenol in the downstream process because it co-distills with phenol during the rectification processes and contaminates the final phenol product. The HA impurity has color-forming tendencies, so trace amounts of HA in the final product phenol renders the phenol product quality unacceptable for many end-use applications, such as bisphenol A and polycarbonate.
Since conventional distillation methods are not effective for removing HA from the phenol product, a number of various chemical treatment methods have been adopted in the industry to achieve its removal via condensation reactions and conversion to higher boiling materials that can be more easily separated from phenol in subsequent distillations. Both homogeneous and heterogeneous processes are described in the prior art. Those processes use both basic and acidic treating agents on the organic streams in the rectification area of the phenol process to promote HA condensation reactions, including sodium hydroxide, amines, ion exchange resins, and zeolites (U.S. Pat. Nos.: 3,335,070, 3,454,653, 3,692,845, 5,502,259, and 6,066,767). However, the use of the chemical treatment processes involving ion exchange resins, alumina, silica-alumina, and zeolites results in the reaction of HA and phenol to form a new impurity, 2-methylbenzofuran (2MBF), which is nearly impossible to separate from phenol by distillation at a product column, so phenol quality suffers. The maximum amount of 2MBF that can be present in the final product without significantly affecting the quality is 20 ppm. The amount of 2MBF formed with ion exchange resins is determined by the concentration of HA in the phenol stream supplied to the ion exchange resin. Typically, the use of ion exchange resins to purify phenol from HA results in the formation of 2MBF in amounts that affect the quality of the phenol product. Zeolites are generally superior to ion exchange resins with respect to catalyst life, but they typically generate even higher amounts of 2MBF.
The use of sodium hydroxide or amines as acidic treating agents on the organic streams in the rectification area of the phenol process to promote HA condensation reactions causes other problems. For example, the use of sodium hydroxide has been found to have the following disadvantages:
The strongly basic sodium hydroxide reacts with the phenol itself to form a sodium phenolate salt. This phenolate salt must be recovered or a loss in phenol yield will result;
The sodium phenolate salt can cause fouling of heat exchanger surfaces resulting in downtime and lost production; and
The sodium phenolate salt can contaminate the final product phenol during the subsequent distillation process causing poor quality product and color.
The use of amines results in the production of waste phenol tar, among other things. The waste products are disposed of by burning, thus forming nitrogen oxides that are released into the atmosphere increasing pollution.
Therefore an improved method is needed for removing carbonyl-type impurities, such as HA, from phenol streams without introducing significant amounts of additional contaminants, such as 2MBF, or other by-products that can foul the machinery or increase pollution levels.
It has been discovered that layered double hydroxides (LDHS) can be effectively employed as catalysts that are useful in the process of converting carbonyl-type impurities, such as hydroxyacetone (HA), contained in a phenol stream into high-boiling derivatives that can be removed from the phenol stream by conventional separation techniques, such as distillation. Thus, in accordance with the invention, a process for converting carbonyl-type impurities, such as hydroxyacetone (HA), contained in a phenol stream into high-boiling derivatives is provided by contacting the phenolic solvent with a layered double hydroxide composition. Preferably, the LDH is a hydrotalcite-type material (HTM) of the formula:
[MII1-xMIIIx(OH)2](Anxe2x88x92)x/n
or a hydrate thereof, wherein MII is a divalent metal cation, MIII is a trivalent metal cation, A is an interlayer anion of charge nxe2x88x92, and x is from 0.12 to 0.8. The phenol can be separated from the high-boiling derivatives using conventional separation techniques, such as distillation, so the invention also provides a process for separating carbonyl-type impurities from a phenolic solvent. The process can be applied in the conventional industrial process for converting cumene to phenol to remove carbonyl-type impurities from the phenol product without introducing significant amounts of additional contaminants, such as 2MBF. A process and a facility for producing purified phenol by converting cumene to phenol are provided. In the conversion of cumene to phenol, the phenol often contains carbonyl-type impurities, such as HA. The phenol and carbonyl-type impurities are reacted in the presence of an HTM to produce high-boiling derivatives. The phenol may be further purified using conventional separation techniques, such as distillation, to separate it from the high-boiling derivatives.